1. Field of the Invention
The present invention relates to a method of calculating a deflection aberration correcting voltage and a charged particle beam writing method. For example, the present invention relates to an electron beam writing method which irradiates an electron beam on a target object while variably shaping the electron beam and a method of acquiring a correcting voltage which corrects deflection aberration generated in pattern writing.
2. Related Art
A lithography technique which leads development of micropatterning of a semiconductor device is a very important process which uniquely generates a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, the circuit line width required for semiconductor devices progressively decreases year after year. In order to form a desired circuit pattern on the semiconductor devices, a high-definition original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam writing technique has an essentially excellent resolution and is used in production of a high-definition original pattern.
FIG. 23 is a conceptual diagram for explaining an operation of a conventional variable-shaped electron beam photolithography apparatus.
A variable-shaped electron writing apparatus (electron beam (EB) writing apparatus) operates as follows. A square, for example, rectangular opening 411 to shape an electron beam 330 is formed in a first aperture 410. In a second aperture 420, a variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 in a desired square shape is formed. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector. The electron beam 330 passes through a part of the variable-shaped opening 421 and is irradiated on a target object 340 placed on a stage. The stage continuously moves in one predetermined direction (for example, defined as an X direction) while writing a pattern. More specifically, a square shape which can pass through both the opening 411 and the variable-shaped opening 421 is written in a writing region of the target object 340 placed on the stage. A scheme which causes an electron beam to pass through both the opening 411 and the variable-shaped opening 421 to form an arbitrary shape is called a variable shaped scheme.
When a predetermined pattern is written on the target object 340, deflection aberration such as deflection astigmatism or field curvature may occur. Development of a technique of correcting the deflection aberration is tried.
As a technique related to deflection aberration, the following technique is disclosed in order to correct optical aberration blur or an electron beam shape size error caused by deflection. That is, voltages applied to electrodes are controlled depending on conditions of a deflected charged beam by use of a rotational symmetry round electron lens capable of independently controlling a control voltage. In this manner, it is assumed that the charged beam is controlled (for example, see Published Unexamined Japanese Patent Application No. 2002-216690 (JP-A-2002-216690)).
As described above, in the writing apparatus, deflection aberration such as deflection astigmatizm or field curvature occurs when a predetermined pattern is written on a target object such as a mask. With an increase in integration density of an LSI in recent years, a circuit line width required for semiconductor devices progressively decreases year after year. For this reason, when dimensional accuracy becomes strict, the deflection aberration becomes dominant as a factor on which dimensional accuracy depends. However, the conventional techniques do not establish a method of exactly inspecting a residual error to check whether a correcting voltage used in correction of the deflection aberration by a deflector or the like is appropriate.